On New Year's Day, a NASA spacecraft is going 'beyond the known world'
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On New Year's Day, just after midnight, NASA's New Horizons spacecraft will fly past a space rock 6.6 billion kilometers from Earth named Ultima Thule. It will be the farthest world we humans have ever visited and seen in detail though robotic eyes.
Ultima Thule — pronounced TOO-lee or THOO-lee, depending on who you ask — is a Kuiper Belt Object, one of perhaps a hundred million small, icy rocks beyond Neptune. Think of the Kuiper Belt like another asteroid belt, only farther away, with worlds ranging from what look like small comets and asteroids up to full-blown dwarf planets. (Pluto is technically a Kuiper Belt Object.)
The term Ultima Thule was used by ancient civilizations to mean the farthest point north, or simply, ‘beyond the known world.’ This will be the farthest object from Earth we've ever visited, so the name is appropriate! Ultima Thule takes a staggering 300 years to orbit the sun.
This is an unofficial name, mind you — the object's real name is 1998 MU68, but that's boring, so the team came up with alternative nicknames and put them to a public vote.
So what do we know about this object beyond the known world? Not much! It's reddish, about 30 kilometers in diameter, and may be actually be two objects orbiting each other, or two objects smooshed together and connected by a small neck, like a peanut.
Let's talk about the flyby. On January 1, New Horizons will snap pics of Ultima Thule as it flies by at — are you ready for this? — 14 kilometers PER SECOND. And even at its closest approach, New Horizons will still be 3500 kilometers away from Ultima Thule!
Let's envision this using a more familiar scale: the continental United States. Ultima Thule is roughly as wide as Washington D.C.— it would just fit within the Beltway. New Horizons will only get roughly as close as the West Coast, and will be traveling fast enough to make it from LA to Seattle in just two-and-a-half minutes.
Oh, and the sharpest pictures we get will come from what's essentially an 8-inch telescope. That actually makes sense, when you think about it; with my 8-inch telescope I can see all sorts of cool things on the moon, and it's about 100 times farther away from me than New Horizons will be from Ultima Thule!
At this point, most people ask me: Can't New Horizons slow down and get a better look? Nope. This is the same spacecraft that flew past Pluto in 2015. Even at the breakneck speeds it's traveling, it still took 9 years for the spacecraft to get to Pluto and three more to get to Ultima Thule. To carry enough fuel to slow down or enter orbit around either object would have required a whole different spacecraft design, and a lot more money — which NASA doesn't have an infinite supply of. There are many other worlds to explore, and performing an initial survey of something like Pluto with a flyby is pretty standard. Flyby data helps scientists come up with new questions — questions that can be answered on future missions with more specialized science instruments.
So why are we visiting Ultima Thule in the first place, and what do we hope to learn?
After New Horizons flew past Pluto in 2015, NASA was left with a perfectly healthy spacecraft speeding out of the solar system. The mission team figured there were bound to be some more Kuiper Belt Objects on New Horizons' path, so they asked for time on the Hubble Space Telescope to look for a few. In 2014, they found what eventually came to be known as Ultima Thule and adjusted New Horizons' course to make a flyby.
But why go to all this trouble to catch a fleeting glimpse of a dumb ol’ rock on the outskirts of the solar system?
Well, many important questions in planetary science ultimately boil down to us humans wanting to know more about the origin of the solar system — and by extension, ourselves. The more worlds we study, the more we can reverse-engineer the processes that shaped the planets.
Scientists think Kuiper Belt Objects probably formed in place -- that is, they didn’t start off in another part of the solar system and get pushed to where they are now. That means they're sort of like time capsules from the formation of the solar system 4.5 billion years ago.
What kind of minerals and ices will we see on Ultima Thule? The answers will tell us what was going on back when the planets were forming, and fill in another piece of the crazy puzzle that is figuring out where we came from. We will hopefully get our first good look at Ultima Thule on New Year's Day, so stay tuned!